Data storage devices have been becoming smaller in size (as well as faster) due to, for example, the continued improvement in the ability to store more information in smaller spaces. For example, over the past twenty years the ability to place more data on magnetic storage media such as magnetized hard-disk drives and/or floppy disks, as well as on optical media (e.g., compact disks “CD's” and more recently, Digital Versatile Disk “DVD's”) has been increasing at a phenomenal pace. The impressive increase in the ability to store more data in smaller areas has been one of the main driving forces for rendering computers, and other electronic devices with reasonably sized memories, accessible to a typical home or small business consumer. Further, the high operating speeds of microprocessors have required stored data in computers to be rapidly accessible (e.g., both the rate at which information is delivered to a microprocessor as well as the amount of time it takes between the time that a microprocessor requests a file and when the first piece of data begins to flow from the file to the microprocessor are important). Magnetic memory has undergone many recent improvements and has been utilized extensively in data storage/retrieval devices because magnetic memory currently provides the least expensive alternative for the fast writing and reading capabilities for data. However, the various currently utilized magnetic technologies face a variety of technical challenges and appear to be headed for a stopping point. Specifically, these various approaches for the storage and/or retrieval of information may no longer be capable of meeting the growing demands of the industry, without experiencing significant technical enhancements.
For applications where speed has historically been less important, various optical technologies have been growing in popularity. Many technical advances have been made in the recording and/or retrieval of information by optical means. In systems which use compact disks (“CD's”), compact disk read-only memory (“CD-ROM's”) and/or Direct Video Disks (“DVD's”), the storage and/or retrieval of information has also been of great interest. For example, the first CD's manufactured were CD-ROM's that are currently capable of storing about 650 MB of data. This equates to about 74 minutes of play-time for music that has been recorded in a typical recording mode.
In particular, the standard current approach for utilizing CD-ROM's, includes the use of a solid state interrogating laser (or in some cases more than one laser) which has a wavelength of about 780 nanometers (0.78 μm). The standard CD-ROM is about 12 cm in total diameter and has a thickness of about 1.2 mm. The standard CD-ROM has information recorded on plateaus (“bumps”) and valleys (“pits”) that spiral from the inside of the disk toward the outside of the disk. The digital data stored in the tracks that comprise the spirals must be separated by enough space (e.g., tracks are typically separated radially by about 1.6 μm) so that when the data is read with an interrogating solid state laser, crosstalk from adjacent tracks does not occur (i.e., recorded information is received from only one track at a time). Accordingly, the placement of more information onto a typical CD has been limited by the required size (e.g., length and width) of the plateaus (“bumps”) and valleys (“pits”). The size of the plateaus and valleys (e.g., typically not less than 830 nanometers in length) has been a function of various factors, including the wavelength of the laser utilized to read the information from the CD.
Various attempts have been made to increase the memory capacity of current CD's, including the stacking of a plurality of disks one on top of the other so as to provide more memory space, as well as other attempts to miniaturize the digitized information stored in the tracks.
The most recent significant improvements in this type of optical storage/retrieval technology have been the creation of the DVD, which is known as the “Direct Video Disk” or the “Digital Versatile Disk”. The first commercial products of DVD's entered the marketplace in late 1997. The DVD technology is similar to the technology in CD's, except that, for example, the wavelength of lasers utilized to read information from DVD's is smaller than that used for CD's, namely, about 635 nanometers or 650 nanometers, compared to about 780 nanometers for CD's. The size of the plateaus (“bumps”) that make up the DVD are about 320 nanometers wide, a minimum of about 400 nanometers long and about 120 nanometers thick. About 740 nanometers separate one track from the next, compared to the about 1600 nanometer separation of tracks in CD's. A standard DVD is physically about the same size as a CD, but has a memory capacity that is about seven times greater than that of CD's. In particular, the memory capacity of a one-sided, one-track, DVD is now about 4.7 GB. However, recent improvements in DVD have allowed digital information to be placed on both sides of a single track, as well as both sides of a double track. In this regard, a first interrogating laser reads the digitized data on a first side of a first track (i.e., in the form of bits arranged in a spiral track that begin in the innermost portion of the DVD and spirals outward). Then, information can be retrieved from the opposite side of the first track in a similar manner from a second laser; however, the spiral track of information typically begins on the outermost portion of the disk and spirals inward toward the center. Accordingly, when dual-track, dual-sided DVD disks are used, the current amount of memory that can be achieved is about 17 GB.
Another optical data storage technique which shows promise is known as holographic memory. The potential for high storage capacity and high storage retrieval rates using the holographic technique is tremendous. In particular, for example, recent work in a system known as Holographic Data Storage System (“HDSS”), has shown that data can be accessed in 100 microseconds or less, which is several orders of magnitude faster than the millisecond retrieval of data in typical magnetic-disk drives. Briefly, in this technology, an optical-interference pattern is created within a desired photosensitive material (e.g., a crystal or a polymer). The optical interference pattern is imprinted as a result of physical changes in such materials. The interference pattern is created by the interaction between an object beam and a reference beam, both of which typically originate from a single light source (e.g., a laser), but are split into two different pathways by a beam splitter. Specifically, the object beam is incident on a target object that contains data, and modifies the object beam, while the reference beam, taking a separate path which leaves it unmodified, interferes with the object beam at the holographic storage medium. When the two beams meet at the holographic storage means, the interference pattern which results from their interaction is stored on or in the holographic storage means. The holographic storage means is later interrogated by a reading or reference beam, which upon interacting with the holographically stored interference pattern, can then recreate the holographic image containing the data originally stored in the object beam.
While the holographic optical technique shows great promise for the future, current industrial emphasis is being placed primarily on improving existing digital optical and magnetic storage/retrieval systems so that more information can be stored in smaller spaces, and retrieval times can be decreased without significantly changing the basic methodology and hardware for the storing and retrieving of information.
With regard to placing more data onto magnetic recording media, effects such as the paramagnetic effect (e.g., magnetic crosstalk between magnetic domains comprising bits) are already beginning to cause problems. Experts have postulated that in coming years, magnetic storage technologies could reach a limit imposed by the superparamagnetic effect (“SPE”). The physical phenomenon known as SPE can occur in a magnetic data storage system when the magnetic spins of electrons in the domains which comprise a bit (e.g., in current technology typically either a “0” or a “1”) become unstable due to, for example, the environmental thermal energy surrounding the bits. Instability of bits occurs when smaller and smaller numbers of domains or atoms are used to comprise a bit and the ability for the domains or atoms to maintain their given spin directions (e.g., corresponding to, for example, a “0” or a “1”) becomes difficult. Non-maintenance of spin directions results in a “flipping” of spins back and forth and thus changing “0's” to “1's” and “1's” to “0's”, etc. Such changing or flipping of spins will result in a corruption of the data or information that the “0's” and “1's” represent. Accordingly, in order for smaller numbers of atoms to be used to form a bit and in order for the bit to be viable, techniques and/or materials for preventing the superparamagnetic effect need to be developed to overcome the deficiencies of the prior art.
Another potential problem in recording information magnetically is that the write head which is used to align magnetic domains in the magnetic storage media may be limited in the ability to impart a required field strength over the entire domain area comprising a bit to cause the magnetic domains to behave as though they have been exposed to a substantially uniform field. In such cases, it is possible that differently oriented domains within a bit (e.g., differently oriented due to being subjected to different magnetic field strengths within a single writing head due to, for example, non-uniformity of the magnetic flux lines emanating from the write head and/or differently oriented because some domains require more energy than other domains to align due to, for example, their location within a bit) may have a higher tendency to become corrupted, as well as adding to signal/noise ratio problems.
One attempt for miniaturizing domains involves the use of so-called “hard” magnetic materials. The use of hard magnetic materials is desirable when compared to “soft” magnetic materials because hard magnetic materials are more likely to maintain their magnetic spin directions when domains comprising the hard magnetic materials are closely spaced. In this regard, various rare-earth and transition elements have been found to be magnetically stable and are thus termed “hard”. Such magnetically stable materials are known to have a higher coercivity, which is typically represented by “Hc”. Stated in an over simplified manner, the higher the Hc value, the greater the resistance of the material to outside influences, such as outside magnetic fields (e.g., the harder it is for material to lose its imprinted spin direction due to an increase in temperature and/or the influence of other magnetic fields, etc.). However, one drawback for utilizing “hard” magnetic materials is that hard magnetic materials are more difficult to magnetize than soft magnetic materials (e.g., in some cases, depending on the particular materials chosen, much more difficult to magnetize). This makes it more difficult to record data initially in hard magnetic materials. There are various known approaches for solving the problem of encoding data into hard magnetic materials which approaches utilize a laser in conjunction with an appropriate magnetic write head. These various approaches have been referred to generally as the “magneto-optical” approach. These magneto-optical approaches effectively reduce the Hc value of the magnetic domains by causing the domains to be locally heated just prior to being subjected to the magnetic write head. Thus, the coercivity (Hc) of the domains is effectively reduced and when such effective reduction in Hc has occurred, a somewhat standard write head, or in some cases a very different write head, can be used to alter favorably the magnetic domains. In other words, the use of a laser, which provides thermal energy to the domains of the hard magnetic material, causes the hard magnetic material to behave in a manner which is similar to a somewhat softer and thus easier to magnetize magnetic material.
Each of the known approaches for utilizing the magneto-optic techniques involves the use of at least one laser and/or at least one laser focusing system. However, one of the common problems facing these magneto-optical approaches is that the lasers that are utilized to soften the hard magnetic material prior to subjecting the hard magnetic material to a magnetic field is that the lasers typically generate excess amounts of heat that can flow to neighboring bits or tracks (e.g., thermal energy is caused to migrate to undesirable neighboring tracks or areas resulting in a potential corruption of stored information). Accordingly, various laser applications and/or storage solutions have been devised to minimize the transfer of heat from the laser to neighboring tracks, and thus minimize the loss of recorded information. However, to date this thermal transfer of laser energy still presents problems to varying degrees in all the prior art approaches.
One interesting technique for the reading of data in connection with one optical-magnetic system is the use of an effect known as the “Kerr effect”, and more particularly, the “magneto-optical Kerr effect”. Briefly, current uses of the magneto-optical Kerr effect involve incident polarized light being reflected from the surface of a magnetic domain in different ways, depending on the orientation of the magnetic domains (e.g., depending on electron spin directions). The changes in the reflected polarized light are made, by algorithms, to correspond to different digitized data. Specifically, when the incident polarized light encounters different magnetic field orientations (e.g., north or south domains comprising a bit which are ordered to represent either a “0” or a “1”) the polarization state of the reflected light is changed.
Another approach to the digital storage of information that shows future promise is known as atomic resolution storage (“ARS”). This approach, similar to holographic techniques, is capable of storing tremendous amounts of information in a small amount of space. In this technique, generally, very small electron probes, which are used to generate electron beams, are formed into an array. The electron probes have tips that are roughly the size of atoms. The electron beams from the electron probes are made to be incident upon a storage medium so that the incident beams cause some sort of physical change in the storage medium (i.e., the medium comprising the computer memory). One example of such a storage medium is a material that is capable of containing at least two stable phases at ambient operating conditions so that an incident electron beam emitted from an electron probe changes the storage material from one phase to the other. In this technique, encoded bits of information are represented by the change in phase of the phase-change storage material. This technique, similar to the magneto-optical technique discussed above, also suffers from the problem of heat flowing between data spots created by the incident electron beams when the spots or bits are initially recorded. Accordingly, one of the challenges faced by this relatively new technology includes reducing the flow of heat between data spots which are created by the array of electron beam generators.
The retrieval of stored information is also a challenge. In this regard, as bits become smaller and include lesser numbers of magnetic domains per bit and/or the domains are oriented differently, (e.g., domains are aligned perpendicular to the substrate containing at least one magnetic surface thereon instead of being parallel to the substrate surface) such bits are capable of being packed more tightly together. Assuming that the bits are not corrupted by their tight packing and/or smaller numbers of magnetic domains and/or non-uniform alignment within a bit, then reading of these tighter packed domains comprising the bits also becomes a challenge which the prior art is still struggling to overcome. Historically, large numbers of magnetic domains were present in each bit which contained digital data. Thus, the resulting or induced magnetic fields were relatively large and various forms of known inductive reading techniques were sufficient to ascertain whether the hundreds or thousands of aligned domains in a bit corresponded to a “0” or a “1”. However, as prior art miniaturization recording techniques progressed, the known inductive reading techniques were typically not sensitive enough to determine accurately the alignment of ever decreasing numbers of domains comprising a bit (e.g., signal to noise problems in the storage and/or retrieval of digital data bits were exacerbated).
The development of magnetoresistive heads, and the subsequent development of giant magnetoresistive heads, has enabled smaller numbers of domains comprising a digital bit to be read accurately. In both of magnetoresistive and giant magnetoresistive heads, the electrical resistance of one or more materials comprising the read head(s) is examined. In particular, both magnetoresistive and giant magnetoresistive heads are made from materials that exhibit small changes in their electrical resistance as a function of magnetic fields created by oriented domains to which such heads are exposed. Giant magnetoresistive heads are two or three times more sensitive than magnetoresistive heads due to their novel structure which includes layering of different materials stacked on top of each other. One problem that continues in these technologies is the presence of magnetization vortices in the recorded domains. Such vortices may result from the difficulty in achieving uniform domain alignment within a bit due to, for example, the difficulty in applying a required magnetic field (e.g., uniform field) to the domains during the recording or writing process.
While use of the magneto-optical Kerr effect and new read heads such as magnetoresistive heads and giant magnetoresistive heads have improved digital data retrieval techniques, further miniaturization is pushing the limits of these systems. Accordingly, additional improvements are necessary in the ability for hardware, combined with suitable programming, to detect even smaller numbers and/or smaller sizes of domains comprising digitized (or analog) data bits. Thus, additional innovations in the detection of stored data are required.
In addition to the storage of information digitally, the possibility or promise of storing information in an analog manner continues to intrigue various investigators. While certain improvements have been made in, for example, the processing of analog information (e.g., the advent of VLSI (Very Large Scale Interrogation) chips, the techniques for the storing of analog information need much improvement. Particularly, while analog computing has been known for several decades, an accurate and fast-paced system for the storage and retrieval of information has continued to elude researchers. In this regard, digital computing has received the greatest amount of attention because of it's relative dependability for the storing and retrieving of information in a “1” or a “0” digitized format. Briefly, digital approaches typically include storing a sampling of the analog information that is to be recorded. The number of samples taken (e.g., such sampling typically occurs in predetermined units of space or time) from the analog source will correspond to the accuracy between the original analog image or sound and the stored digital data (i.e., the more digital samples that are recorded of an original analog image or sound, the more accurate the reproduction of the original analog image or sound will be). These techniques of predetermined quantum amounts of sampling of analog images have been adequate for most digitized applications, however, as the need for more accurate recording and retrieval of information occurs (e.g., in, for example, the fields of computing or determining various engineering and scientific relationships in the following representative areas: gravitational; electrostatic; magnetic; thermal; stress; fluid flow field analysis; wave propagation; image processing; etc.), the availability of computing with more accurate data becomes important. However, the digitization of tighter and and/or smaller sampling amounts from an analog source can result in tremendous amounts of digitized data being stored to represent a small actual amount of analog information. This is one area where analog computing has a distinct advantage compared to digital computing. In particular, an analog computer will store only a single piece of information corresponding to a single sampling area, whereas a digital computer will need to store somewhere between, for example, 8 and 16 bits of data to represent the same single piece of information stored in an analog fashion. The large number of bits required to store digital information corresponds to the requirement to store information in an ASCII or Unicode format. However, in order to escape from the current ASCII or Unicode format, analog storage requires a very large number of different data bits (e.g., data corresponding to much greater numbers than merely “0's” and “1's”) to be stored and retrieved. Current prior art techniques have great difficulty in storing and/or reading bits corresponding to anything other than “0's” and “1's”, let alone the attendant problems of storing and/or reading, for example, a near infinite number of possibilities (e.g., 1, 2, 3 . . . n+1). However, when performing complex calculations, the digital process may result in very slow processing times as well as requiring very large memories. It is for this, as well as other reasons, that analog computing is still very attractive. Thus, while advances in the processing of analog information have been made, reliable techniques for the storage and retrieval of analog information are still being sought without any good solutions currently existing.
As stated above, with regard to digital computing, much of the recent technical emphasis in data storage and retrieval for both optical and magnetic memory enhancement has been on shrinking more information into smaller areas. The ability to place bits, which are the smallest elements of information used by current digital memory systems, into a binary code format, which is a combination of “0's” or “1's”, into a smaller area on, for example, magnetic and/or optical disk storage media (e.g., a disk or a tape) may soon reach a limit. Thus, current technologies for writing and/or reading binary data onto and/or from current storage media will be pushed to the maximum limit. Computer designers are already facing a performance gap whereby processors can process information faster than the information can be retrieved from computer memory.
The majority of the currently proposed approaches for the digital storage of information, suffer from the same problem, namely, that the magnetic and/or optical information which is stored uses a binary code (i.e., a base-2 number system) which is a combination of “0's” and “1's”. The predominance of the use of a “binary” code has been due to, for example, difficulty in distinguishing signals (e.g., a “0” or a “1”) from background noise. In this regard, many techniques have been proposed which use various hardware, as well as algorithms, which attempt to read accurately the stored information as either a “0” or a “1”.
However, certain prior art techniques have been postulated for utilizing codes other than binary. In particular, U.S. Pat. No. 6,154,432, entitled “Optical Storage System” discloses a holographic system which records information in very small spots and postulates that 10 or more digits may be possible to record on a single bit. Accordingly, this holographic technique discloses codes higher order than binary.
Further, for example U.S. Pat. No. 5,450,363, entitled “Gray Coding for a Multi Level Cell Memory System” discloses the use of a so-called “gray code” approach (also known as “gray scale” by others) for data storage. This approach also uses a system which is higher order than binary. In particular, reference is made to the storage of multiple bits of information in a single memory cell thus creating a multi-level cell.
Still further, U.S. Pat. No. 6,061,005, entitled “Encoding of Data”, discloses a method of encoding data on magnetic cards which uses symbology other than binary, such as trinary, quaternary or even higher symbology, for the recording of information.
However, while various techniques have been postulated for systems which use codes higher than binary, none of such codes have been commercially adopted due to, for example, signal to noise ratio problems, etc. In particular, reading errors can occur due to lack of contrast between data values. Such lack of contrast can be caused by random noise (e.g., vibrating inaccurate positioning of recording/reading heads, fidelity loss during recording, etc.) and determinate variations. Accordingly, a need exists for techniques which can be commercially viable which can use codes reliably that are higher order than traditional binary codes for the storage and/or retrieval of information.
A very particular combination of “0's” and “1's” is known as the American Standard Code for Information Exchange (i.e., the ASCII code) which assigns a unique code number between 0 and 127 to each of the 128, 7-bit, binary number characters. Table 1 below shows in table form the current ASCII characters arranged by Hexidecimal digits (i.e., 128 different encoding combinations of groups of seven bits). Reading within the Table from left to right and then down, the first 32 values are codes which correspond to various computer control functions such as line feed, carriage return, etc. The 33rd value corresponds to the “space” character. Values 34-48 correspond to symbols and punctuation marks. Values 49-58 correspond to digits, and so on, until reaching value 128, which corresponds to “delete”. In addition, each of these values also has a corresponding hexidecimal character. For example, the hexidecimal digit corresponding to the “space” character is “20”, while the hexidecimal digit corresponding to the letter “n” is “6E”, and so on.
TABLE 1000102030405060708090A0B0C0D0E0F00NULSOHSTXETXEOTENQACKBELBSTABLFVTFFCRSOSI10DLEDC1DC2DC3DC4NAKSYNETBCANEMSUBESCFSGSRSUS20!“#$%&‘()*+,−./300123456789:;<=>?40@ABCDEFGHIJKLMNO50PQRSTUVWXYZ[\]{circumflex over ( )}—60{grave over ( )}abcdefghxjklmno70pqrstuvwxyz{|}~DEL
These 128 characters are enough characters for North American English to be stored and/or retrieved, but are not enough for many other languages (Note: In ASCII, the eighth bit is unused, and is thus normally set to “0”). To represent more than 128 characters, 8-bit (rather than 7-bit) binary numbers are utilized. For each digit in these eight bits there are two choices for the digit, either “0” or “1”. This results in a possibility of an additional 128 characters or a total of 256 different combinations of “0's” and “1's” (i.e., 28). Accordingly, the current data storage approaches utilize these 256 combinations of “0's” and “1's”. However, these 8-bit numbers still do not provide enough room for all characters that need to be used in the world (e.g., certain Asian languages have thousands of characters each). In addition, there is no universal agreement in the world on what all the characters should be, whether referring to the 128 characters, or the 256 characters, or any number of characters beyond these.
However, certain approaches for dealing with all the various languages in the world, which collectively contain many thousands of characters, are beginning to utilize something-referred to as the “Unicode”, which uses a 16-bit character set. In order to adopt something similar to the Unicode, even greater strain will be placed on current memory techniques.
Whether using an 8-bit, 16-bit, or some other approach, all such approaches have been limited primarily to using a binary system of data storage. However, due to: (1) the impending size barrier for the storage of information on, for example, magnetic, magneto-optic and/or optical media; (2) the performance gap between how fast a processor can process information versus how fast a processor can access information; and (3) the goal for a universal adoption of a common set of characters throughout the world, a different approach for the storage of information, either by digital or analog approaches, is clearly needed. The present invention satisfies the current and future data storage needs by using different approaches for the storage and/or retrieval of data; and/or different codes that use a code higher than the current “base-2 code”.